Do Zebras Get Less Spam Than Aardvarks?

Cambridge University security expert Richart Clayton discovered a link between the first letter of your e-mail address and the amount of spam you receive:

The study (.PDF), titled "Do Zebras get more Spam than Aardvarks?" analyzed traffic logs from the U.K. ISP Demon Internet. The data analyzed was from the period Feb. 1st - March 27th of 2008.

In the study, Clayton noted that those whose local part of their email address (this is the portion to the left of the "@") begins with "A" receive about 50% spam and 50% non-spam. Clayton called this group aardvarks. When the local part begins with "Z" (call them zebras) about 75% is spam.

You're probably saying, eh? This makes no sense based on what was said earlier. Ah, but it does.

The reason more of the zebra email is spam is because so few actual email addresses start with "Z". Thus, the real portion of email is smaller. If you only look at legitimate email addresses, the picture changes: 20% of email addressed to zebras is spam, 35% of aardvarks is spam.